Aerated frozen products generally require the mixing of selected liquid ingredients with a prescribed volume of air and freezing of the resultant mixture and dispensing of the finished product. The desirability of the finished product is often related directly to the manner and to the degree in which the air is metered and blended with the liquid ingredients of the mixture and the manner in which the blended mix is frozen. The prior art is replete with examples of apparatus for dispensing ice cream and other semifrozen dairy products such as soft ice cream and frozen yogurt.
Usually in such dispensers, the liquid mix containing, in the case of ice cream, ingredients such as cream, milk, condensed milk, syrup, etc. is delivered to a freezing chamber containing air or another non-toxic gas. In the freezing chamber, the mixture is slowly frozen and mechanically agitated by blades or the like to incorporate the air or gas in the mixture. This aeration is especially important and produces an increase in bulk corresponding to a decrease in the product specific gravity, thereby providing what is referred to in the ice cream industry as "over-run". The slow freezing and continuous agitation of results in the formation of ice crystals and particles of varying size which can detract from the palatability of the resultant product.
The chamber typically serves both as the means of freezing and as a reservoir from which individual servings are withdrawn. When the ice cream is partially frozen to the proper consistency, it is pumped or extruded from the freezing chamber to the dispenser outlet for delivery, on demand, to containers such as cups and cones. Examples of such apparatus are disclosed in U.S. Pat. Nos. 3,904,085; 3,954,126 and 4,201,588.
The prior apparatus do not necessarily achieve close control of over-run, which is a prime factor affecting product palatability and profit in the manufacture of ice cream and similar products. If there is not enough aeration in the finished product, not only may the product be so dense as to be unpalatable, but also more liquid mix is required to make a given volume of the product, thereby lowering profit. On the other hand, if there is too much air in the finished product, the product may be considered too "fluffy" and of lower quality and value. Also, in many states there are regulations against providing excessive over-run in certain products to protect the consumer from being charged for a product that consists largely of air.
Conventional dispensers are usually dedicated to dispensing one or two flavors of product and, in some cases, a combination ("twist") of the two. For example, in an ice cream shop, there may be one machine with two separate freezing chambers for making and dispensing chocolate and vanilla ice cream, a second two-chamber machine for making and dispensing strawberry and banana ice cream, a third machine dedicated to making and dispensing coffee and frozen pudding flavors, and so on. The reason for this is that each chamber typically contains a volume of ice cream greater than is required for a single serving. In order to dispense a different flavor ice cream, that chamber must be emptied before the new flavor can be made in that chamber and appear at the outlet of the dispenser; additionally, the vat of preflavored mix from which the material being aerated and frozen is drawn must also be cleaned. While high volume ice cream shops and confectionery stores may have sales to justify the presence of several dispensing machines dispensing many different products, smaller sales outlets can usually only afford one or two such machines and are thus restricted in the number of flavors that they can offer to customers.
Further, because the product is typically formed in a quantity that is greater than that to be dispensed at any one serving, the excess product remains in the chamber after formation and until the next serving is required. The excess is thus subjected to further mechanical beating by any blades in the chamber, as well as to excess freezing which promotes crystallization. Because of the quantity of the premixed flavors, and the continuous freezing and beating of several quarts of the product, the freshness and palatability of the product may be adversely affected in stores with slow sales of the product.
Another disadvantage of the prior dispensers is that they have many interior surfaces and moving parts that are difficult and time-consuming to clean and to maintain. At the end of each day or at other intervals prescribed by local Health Department regulations, each dispenser must be purged of any remaining product, and its chamber walls, pumps, and other internal parts cleaned thoroughly to prevent growth of bacteria that could contaminate product being delivered by the dispenser. Not only is the cleaning operation expensive in terms of downtime, it is also costly in terms of product waste and is an unpleasant and difficult job to get employees to do properly.
There have been attempts to produce and dispense aerated frozen products on a continuous basis by atomization. In one example of this type of dispenser, disclosed in U.S. Pat. No. 2,594,422, a liquid mix and a liquid refrigerant are mixed in a mixing chamber and fed through a rotary emulsifier which forms a single liquid emulsion. The emulsion is then jetted from a spray nozzle, into a separating chamber where the liquid refrigerant evaporates, effectively freezing adjacent droplets of mix and thereby transforming them into flakes or a fine powder. Groups of flakes then agglomerate into larger particles containing an interior void. The refrigerant adsorbed on the interior surfaces of the void may further expand in the separating chamber to increase the bulk of the particles and thus decrease their density. The liquid refrigerant evaporated in the separating chamber is drawn off and reused. The frozen particles fall into the chamber of a screw-type extruder which compresses the particles at a controlled rate to give the final product the desired density and drives the frozen product to the dispenser outlet.
The over-run is formed by, and limited by, the void space between flakes formed by mechanical agglomeration as opposed to actual entrapment of air within the interior of an individual droplet. Thus, even though that patented dispenser uses atomization to make an aerated frozen product, the over-run is determined by the amount of liquid refrigerant adsorbed in the liquid mix before it is fed to the separator. In addition, the extruder is required to further reduce overrun and improve body texture.
Also that patented apparatus, like the other dispensers described above, has various internal surfaces and moving parts which must be cleaned in order to keep that dispenser in a sanitary condition. Moreover, there is always a supply of frozen product in the extruder chamber. As described above, this makes it impossible to change quickly from one product flavor to another and, if there is a change without disassembling and cleaning the machine, this results in a mixing of flavors.